intelligibility vs perspicuity

intelligibility

noun
  • That which is intelligible; the degree to which something is intelligible. 

  • The quality of recorded speech of every word being understandable. 

perspicuity

noun
  • Clarity, lucidity, especially in expression; the state or characteristic of being perspicuous. 

  • Transparency; translucence. 

  • Perspicacity; insight. 

How often have the words intelligibility and perspicuity occurred in a corpus of books? (source: Google Ngram Viewer )